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• SinuShunt
  Marek Czosnyka
  Published on: 19 October 2004

• Published on: 19 October 2004

  SinuShunt

  • Marek Czosnyka, reader
  • Other Contributors:
    • Zofia Czosnyka, John D. Pickard

  Dear Editor,

  We have read the paper by Eklund et al with great interest. It is essential to learn about the hydrodynamic properties of new designs of hydrocephalus shunts assessed independently on the manufacturer.

  Uncomplicated hydrocephalus is easy to manage, but in patients with a history of multiple shunt revisions, hydrodynamics of CSF drainage through the shunt really matters. The shunt should...

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  Dear Editor,

  We have read the paper by Eklund et al with great interest. It is essential to learn about the hydrodynamic properties of new designs of hydrocephalus shunts assessed independently on the manufacturer.

  Uncomplicated hydrocephalus is easy to manage, but in patients with a history of multiple shunt revisions, hydrodynamics of CSF drainage through the shunt really matters. The shunt should be carefully matched to the dynamics of the patient's own CSF circulation; the importance of such an approach has been clearly discussed by the authors.

  The UK Shunt Evaluation Laboratory (Cambridge, UK) conducted a similar program of evaluation of SinuShunt in 2003 [1]. We tested three samples of SinuShunt in a computer controlled rig, according to the set test protocol, compatible (but extending beyond) ISO 7197 standard. All the tested shunts demonstrated mechanical durability over the period of testing (35 days) and excellent stability of hydrodynamic performance over a controlled 28 day period.

  The pressure-flow performance curves, operating, opening and closing pressures were stable, with minimal scatter. Operating pressure was low, within the range 1-3 mm Hg. The valve demonstrated a hydrodynamic resistance within the range of normal resistance to CSF outflow (around 9 mm Hg/(ml/min)), i.e. greater than the majority of the contemporary differential pressure valves. This may help to reduce a risk of overdrainage due to nocturnal vasogenic waves. Small particles (of diameter bigger than erythrocytes- 25 ƒÝm ) were found to increase shunt resistance only temporarily. After being washed out spontaneously, the valve resumed normal functioning. Shunt is MRI compatible (3 Tesla magnet). We did not find any reflux, neither at high nor low reflux pressures.

  The major benefit of the SinuShunt is that after implantation, the inlet of CSF (ventricles) and the outlet (transverse sinus) are on the same level regardless body position. This may help to substantially reduce a risk of overdrainage related to body posture (so called siphoning).

  From the point of view of its bench hydrodynamic performance, the SinuShunt after proper implantation should work as a physiological valve - able to restore normal CSF circulation. These properties, found in the laboratory condition should be confirmed by future clinical trial. However, our major reservation concerns shunt function in-vivo. Is transverse sinus pressure always low and closely related to central venous pressure? Recently we have heard that in benign intracranial hypertension this pressure may be grossly elevated [2]. Earlier studies related to head injury also demonstrated elevation of cerebral sinus venous pressures when ICP was elevated [3]. Moreover, in mixed group patients with intracranial hypertension blood flow velocity in cerebral sinuses negatively correlated with directly measured ICP [4]. Blood flow velocity measurement has been proposed for non-invasive assessment of ICP. Therefore, it is not impossible that transverse sinus pressure can increase when ICP rises also in hydrocephalus, impeding CSF drainage through the SinuShunt. It is, more likely in acute hydrocephalus than in NPH. However the influence of dynamic elevations of ICP in NPH (nocturnal B waves) on clinical symptoms is not fully understood.

  Implantation of the differential valve is supposed to limit magnitude of these waves. If vasogenic elevations of ICP may cause similar elevations in the transverse sinus pressure, SinuShunt would not be able to cancel them through accelerated CSF drainage, as the differential pressure through the shunt would stay constant. These are hypothetical reservations, but on the basis of what we know, the shunt should be used cautiously in hydrocephalus, where elevations (both static and dynamic) of CSF pressure may be responsible for a part of clinical symptoms.

  References

  (1). Czosnyka Z, Czosnyka M, Pickard JD. New shunts in the UK Shunt Evaluation Laboratory. Proceeding of the British Neurosurgery Research Group Meeting. Br J Neurosurg 2003. 17:477-497

  (2). Higgins JN, Owler BK, Cousins C, Pickard JD. Venous sinus stenting for refractory benign intracranial hypertension. Lancet. 2002. 19;359(9302):228-30

  (3). Marmarou A, Maset AL, Ward JD, Choi S, Brooks D, Lutz HA, Moulton RJ, Muizelaar JP, DeSalles A, Young HF: Contribution of CSF and vascular factors to elevation of ICP in severely head injured patients. J. Neurosurg. 1987. 66:883-890

  (4). Schoser BG, Riemenschneider N, Hansen HC. The impact of raised intracranial pressure on cerebral venous hemodynamics: a prospective venous transcranial Doppler ultrasonography study. J Neurosurg. 1999. 91(5):744-9.

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  Conflict of Interest:
  None declared.

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